The resolution of an image is determined by the physical characteristics of the sensor that is used to capture the image. In some resolution enhancement approaches, the spatial dimension of an image is increased by interpolating between pixel values of a single image to generate an enhanced image. Both linear and non-linear interpolation techniques have been applied to a single image to produce an image with a higher spatial dimension than the original image. In these resolution enhancement techniques, however, the overall information content in the enhanced image is the same as the original image: the pixel number is increased, but the resolution is not improved. In other approaches, image resolution is increased by obtaining multiple displaced images of the scene and combining the information from the multiple images into an enhanced image. The process of reconstructing an image from several displaced images of the same scene often is referred to as “super resolution”. In these resolution enhancement techniques, the overall information content in the enhanced image may be greater than the information content in the individual original images.
In some super resolution methods, one of the lower resolution images in a sequence of lower resolution images is designated as a reference image. The coordinate frame of the reference image is up-projected to the higher resolution level to define the coordinate frame of the higher resolution image. Motion vectors between the reference image and each of a selected number of lower-resolution images neighboring the reference image in the multi-image sequence are estimated. The motion vectors then are up-projected to the coordinate frame of the higher resolution image. The up-projected motion vectors are used to re-map the neighboring images to the coordinate frame of the higher resolution image. Next, the coordinate frame of the higher resolution image is populated with pixel values that are computed based on combinations of pixel values from the re-mapped lower resolution images. In some approaches, a non-linear interpolation technique is used to reconstruct the higher resolution image from the re-mapped pixel values.